FIG. 1 is an exemplary view illustrating a structure of an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) system, a mobile communication system applicable to the related art and the present invention.
The E-UTRAN system illustrated in FIG. 1 has been evolved from the related UTRAN system, for which the 3GPP (3rd Generation Partnership Project) is proceeding with the preparation of the basic specifications applicable thereto. The E-UTRAN system can be classified as an LTE (Long Term Evolution) system.
The E-UTRAN system includes basic stations (hereafter, referred to as eNode Bs or eNBs) 21, 22, 23, The eNBs 21, 22, 23 are connected with each other through an X2 interface. The eNBs 21, 22, 23 are connected with a terminal (User Equipment; hereafter, abbreviated to UE) 10 through a radio interface, and connected with an EPC (Evolved Packet Core) 30 through an S1 interface.
Layers of a radio interface protocol between the terminal 100 and a network can be divided into an L1 (first layer), an L2 (second layer) and an L3 (third layer) based upon three lower layers of an open system interconnection (OSI) standard model that is well-known in the art of communication systems. A physical layer belonging to the first layer provides an information transfer service using a physical channel, and a radio resource control (hereafter, abbreviated to RRC) layer positioned at the third layer serves to control radio resources between the terminal and the network, for which the RRC layer exchanges an RRC message between the terminal and the network.
FIG. 2 illustrates a structure of the radio interface protocol between the terminal and an UTRAN (UMTS Terrestrial Radio Access Network) based upon a 3GPP radio access network standard. And, FIG. 3 is an exemplary view illustrating a physical channel.
The radio interface protocol illustrated in FIG. 2 horizontally includes a physical layer, a data link layer and a network layer. And, the radio interface protocol is vertically divided into a user plane for transmitting data information and a control plane for transmitting control signals.
The protocol layers of FIG. 2 can be divided into an L1 (first layer), an L2 (second layer) and an L3 (third layer) based upon the three lower layers of open system interconnection (OSI) standard model that is well-known in the art of communication systems.
The physical layer, the first layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected with a medium access control layer located at a higher level through a transport channel, and transfers data to the medium access control layer via the transport channel.
Meanwhile, between different physical layers, namely, between physical layers of a transmission side and a reception side, data is transferred via the physical channel. The physical channel is modulated by an OFDM (Orthogonal Frequency Division Multiplexing) manner, and uses time and frequency as a radio resource.
The second layer is divided into two lower layers. That is, the second layer is divided into the medium access control (hereafter, abbreviated to MAC) layer and a radio link control (hereafter, abbreviated to RLC) layer. The MAC layer provides a service to the RLC layer, an upper layer, via a logical channel. The RLC layer reliably supports a data transmission. Here, a function of the RLC layer can be implemented as a function block within the MAC layer. In this case, the RLC layer may not be present.
Meanwhile, through it is not illustrated, the second layer further includes a PDCP layer. The PDCP layer performs a header compression function for reducing a size of an IP packet header that is relatively large-sized and has unnecessary control information so as to implement an effective transmission in a radio section having a narrow bandwidth at the time of transmitting an IP packet such as IPv4 or IPv6.
A radio resource control (hereafter, abbreviated to RRC) layer belonging to the third layer is only defined in the control plane, and controls logical channels, transport channels and the physical channels in relation to the configuration, reconfiguration, and release of the radio bearers (abbreviated to RBs). Here, the RB signifies a service provided by the second layer for data transmission between the terminal 10 and the UTRAN. If there is an RRC connection between the RRC layer of the terminal 10 and the RRC layer of the radio network, the terminal 100 is defined to be in an RRC connected mode, and if there is not the RRC connection, the terminal 100 is defined to be in an RRC idle mode.
An NAS (Non-Access Stratum) layer as an upper layer of the RRC layer performs functions such as a session management and a mobility management.
Meanwhile, hereafter, the physical channel, the transport channel and the logical channel will be explained in detail.
First, one cell configured by each eNB 21, 22, 23 is established to have one of the bandwidths 1.25 Mhz, 2.5 Mhz, 5 Mhz, 10 Mhz, 20 Mhz and the like so that an uplink or downlink physical channel is provided to multiple terminals. Here, different cells may be established to have bandwidths different from each other.
With reference to FIG. 3, the physical channel includes multiple sub-frames on a time axis and multiple sub-carriers on a frequency axis. Here, one sub-frame includes a plurality of symbols on the time axis. And, one sub-frame includes a plurality of resource blocks, and one resource block includes a plurality of symbols and a plurality of sub-carriers. Also, each sub-frame can use specific sub-carriers of specific symbols (e.g., first symbol) of corresponding sub-frame for a PDCCH (Physical Downlink Control Channel), namely, an L1/L2 control channel. One sub-frame is 0.5 ms, and TTI (Transmission Time Interval), unit time for transmitting data, is 1 ms corresponding to two sub-frames.
And then, the transport channel is divided into a downlink transport channel for transmitting data from the network to the terminal and an uplink transport channel for transmitting data from the terminal to the network. The downlink transport channel for transmitting data from the network to the terminal includes a broadcast channel (hereafter, referred to as BCH) for transmitting system information, a paging channel (hereafter, referred to as PCH) for transmitting a paging message, and a downlink shared channel (hereafter, referred to as SCH) for transmitting a user traffic or a control message. Downlink multicast, traffic of a broadcast service or the control message may be transmitted through the downlink SCH or through an additional downlink multicast channel (MCH).
The uplink transport channel for transmitting data from the terminal to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink shared channel (SCH) for transmitting the user traffic and the control message.
Meanwhile, the logical channel includes a BCCH (Broadcast Channel) for broadcasting system control information, a PCCH (Paging Control Channel) for transmitting call information, a CCCH (Common Control Channel) for transmitting control information between the terminal and the network, an MCCH (Multicast Control Channel) for a multimedia broadcast/multicast service, an MTCH (Multicast Traffic Channel) for the multimedia broadcast/multicast service, etc. The BCCH is mapped to the BCH of the transport channel, and the PCCH is mapped to the PCH of the transport channel.
Hereafter, the multimedia broadcast/multicast service (MBMS) will be explained in detail.
The MBMS denotes that a streaming or background service is provided to a plurality of terminals using a downward-dedicated MBMS bearer service. The MBMS bearer uses a point to multipoint radio bearer service and a point to point radio bearer service in the UTRAN.
The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service to transmit multimedia data to all users in a broadcast area. Here, the broadcast area relates to an area in which the broadcast service is available. The MBMS multicast mode is a service for transmitting multimedia data only to a specific user group in a multicast area. Here, the multicast area relates to an area in which the multicast service is available. The multicast area and the broadcast area are called as a service area.
A radio network for providing the MBMS service provides an MCCH (MBMS Control Channel) and an MTCH (MBMS Traffic Channel) as logical channels. The MCCH channel is used to transmit control information for an MBMS transmission to the terminal, the MTCH channel is used to transmit the MBMS service to the terminal.
The MBMS service includes one session or a plurality of sessions. Only one session can exist in one time interval. The radio network can transmit an MBMS notification so as to inform session start of the MBMS service or modification of the MBMS control information. Here, the notification is transmitted via the MCCH channel. Meanwhile, the radio network informs the terminal of whether or not the MBMS notification or the control information for a specific service is modified, via a physical channel, an MICH (MBMS notification Indicator Channel).
Meanwhile, the MBMS service can be divided into a multi-cell service for providing a plurality of cells with the same service and a single cell service for providing one cell with the same service. The multi-cell service is transmitted via a transport channel, namely, the MCH, and the single cell service is transmitted via a transport channel, namely, a DL SCH channel. When receiving the multi-cell service via the MCH channel, the terminal can receive the multi-cell service by combining the same multi-cell services transmitted from multiple cells by an MBSFN (MBMS Single Frequency Network) manner.